1. Field
The present disclosure pertains to the field of cache memories. More particularly, the present disclosure pertains to a new cache architecture using a dynamic random access memory (DRAM) or the like and methods of mapping cache entries into the memory.
2. Description of Related Art
Cache memories generally improve memory access speeds in computer or other electronic systems, thereby typically improving overall system performance. Increasing either or both of cache size and speed tend to improve system performance, making larger and faster caches generally desirable. However, cache memory is often expensive, and generally costs rise as cache speed and size increase. Therefore, cache memory use typically needs to be balanced with overall system cost.
Traditional cache memories utilize static random access memory (SRAM), a technology which utilizes multi-transistor memory cells. In a traditional configuration of an SRAM cache, a pair of word lines typically activates a subset of the memory cells in the array, which drives the content of these memory cells onto bit lines. The outputs are detected by sense amplifiers. A tag lookup is also performed with a subset of the address bits. If a tag match is found, a way is selected by a way multiplexer (mux) based on the information contained in the tag array.
A DRAM cell is typically much smaller than an SRAM cell, allowing denser arrays of memory and generally having a lower cost per unit. Thus, the use of DRAM memory in a cache may advantageously reduce per bit cache costs. One prior art DRAM cache performs a full hit/miss determination (tag lookup) prior to addressing the memory array. In this DRAM cache, addresses received from a central processing unit (CPU) are looked up in the tag cells. If a hit occurs, a full address is assembled and dispatched to an address queue, and subsequently the entire address is dispatched to the DRAM simultaneously with the assertion of load address signal.